Patent GB-1435016-A (GB)
Title: Pressure sensitive recording systems
IPC: B41M5/165
Filed: 1973-07-23
Abstract: 1435016 Pressure sensitive recording sheets KANZAKI PAPER MFG CO Ltd and TORAY INDUSTRIES Inc 23 July 1973 [22 July 1972] 34974/73 Heading D2B A pressure sensitive recording sheet comprises a support sheet having disposed on at least one of its surfaces a microcapsulated oil solution of a colourless dye, andlor a colour former reactive with the colourless dye to produce a colour image, the support sheet comprising fibrous material, at least a part of which is synthetic (including cellulose fibres having vinyl polymers formed on or within them or having alpha-olefin polymers deposited on them), and said support sheet having a coefficient of tetralin penetration rate (K) of 600 X 10<-3> cm/min or less. The value of K is derived from the formula h = Kt<¢>, where h is the height to which tetralin contacting the bottom of a vertical strip penetrates in time t. The synthetic fibrous material preferably has a specific surface area of at least 0.7 cm<2>/g. The fibrous material may be wholly synthetic, or may include cellulose fibres. In one preferred form of the invention, the synthetic fibrous material comprises at least 50% by weight of alpha-olefin units, the alpha-olefin units preferably forming at least 4% by weight of the total amount of fibrous material. Suitable alpha-olefinic polymers for spinning to form the synthetic fibres include polyethylene, polypropylene, poly-1-butene and poly-4-methyl-1-pentene; copolymers of alphaolefins such as poly-(ethylene-propylene); copolymers of alpha-olefins with other monomers; and graft copolymers and cross-linked products of the above polymers. Mixtures of these polymers with each other and with other polymers may also be spun to form the synthetic fibres. Synthetic fibres made from a polyalpha-olefin and having a hydrophilic component may be used, such fibres being produced by spinning an alpha-olefin polymer or copolymer into which a hydrophilic component has been incorporated by the blending with a hydrophilic polymer and/or by graft polymerisation. Suitable hydrophilic polymers include polyvinyl alcohol; polyacrylamide; polyethyleneoxide; polyethylene glycol; carboxymethyl cellulose; random, graft or block copolymers containing vinyl monomer units having a hydrophilic radical or vinyl monomer units to which hydrophilic radicals can be introduced by hydrolysis; ; and copolymers of an alpha-olefin with a vinyl monomer having a hydrophilic radical or a vinyl monomer to which a hydrophilic radical can be introduced by aftertreatment. Suitable vinyl monomers include vinyl acetate, acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, acrylamide, allyl alcohol and butene-tri-carboxylic acid. Among the monomers which may be introduced into the poly-alpha-olefin by graft polymerisation are vinyl monomers having a hydroxyl group and/or a carboxyl group, and vinyl monomers that can acquire a hydroxyl or a carboxyl group by hydrolysis. Examples of such monomers are vinyl acetate, acrylic acid, methacrylic acid, methyl methacrylate, allyl alcohol and butene-tricarboxylic acid. Monomers such as acrylonitrile, vinyl chloride and acrylamide may also be present during the graft polymerisation. A preferred fibre is one formed by emulsion flush spinning if a mixture of 50-99% by weight of a alpha-olefin polymer or copolymer e.g. polypropylene, and 50-1% by weight of polyvinyl alcohol. Other spinning techniques which may be used are flush spinning, uniaxial stretching and splitting, solution shearing and centrifugal spinning to produce the fibre, which may be subjected to beating or refining. In a second preferred form of the invention, the synthetic fibrous material comprises at least 60% by weight of vinyl alcohol units, and the vinyl alcohol units form at least 15% by weight of the total fibrous material. The fibres may be spun from a spinning material obtained by hydrolysing polyvinyl acetate or a copolymer of vinyl acetate with vinyl chloride, an acrylic ester or a methacrylic ester. The spinning material may also include starch, casein, cellulose derivatives and polyacrylic acid. The fibrous material may be subjected to beating. In a third preferred form of the invention, the synthetic fibrous material is prepared by polymerising at least one of vinyl acetate, acrylic acid, acrylic ester, acrylamide, methacrylic acid, methacrylic ester and methacrylamide onto cellulose fibres or by depositing a polymer or copolymer of at least one alpha-olefin onto natural or synthetic fibres. Thus in examples 6 and 7, polyethylene is deposited from an emulsion onto wood pulp fibres and acrylic fibres respectively using aluminium sulphate. The synthetic fibrous material may be subjected to beating, and the polymer component is preferably at least 3% by weight of the total fibrous material. The support sheet may include bamboo pulp, straw pulp, linen fibres, bleached hard wood kraft pulp, bleached soft wood kraft pulp, inorganic fillers, sizing agents, defoaming agents, dyes and adhesives. The support sheet may be coated on one side (example 1) with macrocapsules of a solution of crystal violet lactone and benzoyl leucomethylene blue in isopropyl naphthalene, the encapsulating material being gum arabic and gelatin. The support sheet may 'be coated on the other side (example 1) with an active clay and styrene butadiene latex, the coating being covered by a yellow dye.